PM_2.5 and monitoring sites

The Environmental Targets (fine particulate matter) (England) Regulations 2023 set two PM_2.5 targets for England to be met by the end of 2040. Interim targets for 2028 were published in the Environmental Improvement Plan 2023. The two legislative targets, both to be met by 2040 are:

• Annual mean concentrations of PM_2.5 to be 10 µg m^-3 or lower
• Population exposure to PM_2.5 to be reduced by 35% compared to 2018 levels

The two targets are designed to work together to drive actions that both reduce concentrations where it is highest and reduce the pollution that everyone in the country experiences.

Whilst the targets apply across the country, progress towards both targets is assessed using measurements of PM_2.5 concentrations from the Automatic Urban and Rural Network (AURN) monitoring network, which is being expanded to support this assessment. Information on how PM_2.5 is measured can be found here.

Minimum numbers of monitoring stations

The new targets legislation set a minimum number of PM_2.5  sites in England to be monitoring PM_2.5 as part of the AURN from 1st January 2028. The numbers of monitors needed is determined by the population size for each zone and agglomeration and is calculated according to the categories of 'total sites', 'near source sites' and 'urban background/suburban' sites as tabulated below:

As the population grows the number of sites required can change, so the year for which the population for each zone/agglomeration is assessed is important. 

The original calculations of the number of PM_2.5 monitors required for each zone and agglomeration as part of the overall expansion programme were based on the available population statistics at the time (year 2020), at the point at which the regulations were set. Since then, the population size for many of the zones and agglomerations has increased and the Office for National Statistics (ONS) has predicted that the total population in the UK will increase by 3.6 million between 2021 and 2027. 

However, the time it can take to establish a new monitoring station ranges from 1-3 years depending on the individual circumstances of the site and the development steps required, for example gaining planning permission, leases or installing electrical connections etc.

Calculating the PM_2.5 monitoring site numbers using population changes in the preceding months or years of the legal deadline of 31st December 2027 will give little or no time to implement any additional sites that maybe needed.

Therefore, the calculation of the minimum number of monitoring sites will be fixed in 2024 and will be based on the ONS population statistics for 2022. This allows suitable development time to ensure that any additional monitoring stations can be in place by the legal deadline.  We will continue to review additional requirements on a regular basis to ensure that the network keeps aligned to future population increases over time.

Calculation of minimum numbers of monitoring stations

The numbers of monitors required for each zone and agglomeration has been calculated by the population size using ONS population statistics for 2022. This has been tabulated below according to the categories of 'total sites', 'near source sites' and 'urban background/suburban' sites as stipulated by the legislation. 

For resilience purposes, the ongoing PM_2.5 monitoring expansion programme has factored in a 2% increase in population levels from 2022 in each zone and agglomeration.